On widening gap between doses

It could let us vaccinate nearly twice as many people in next few months.

I’ve shown cumulative doses administered, with 1st dose graph lagged by 6-weeks. Till April 23, curves match perfectly, reflecting 2nd doses being delivered 6-weeks after 1st dose (on average). However, over past three weeks, second doses are behind schedule. Compared to earlier matching curves, we’re 20 million second-doses behind.

Plan A: persist with 6-8 week gap. Between now and end-June, we’ll have to administer 90 million second doses in 45 days. That’s higher than our recent vaccination pace (across both doses combined). Further, nearly 50% of incremental vaccine supply will be blocked for 2nd doses (which is already the case over past fortnight). Next few weeks will be particularly frustrating as our 3M/day early-April pace (on 1st doses) will come due for 2nd doses. Our backlog could cross 50M in a few weeks. That’s 50M frustrated people.

Plan B: extend gap to 12-16 weeks (which government announced yesterday). Let’s accept medical soundness and international precedent of proposal. Plan B numbers look much better. No incremental 2nd doses come due till July first half. In an optimistic scenario, vaccine supply could be enough to administer 1st doses to nearly 200M people over next 8 weeks. Obviously, our covid-lockdown-impacted pace is nowhere near that. If we get breathing room (literally) in a few weeks, pace can improve. At the least, we won’t be constrained by second doses crowding out new vaccinations. 200M is a big addition to current 140M vaccinated people. Assuming half of incremental vaccines go to 45+ age-group, we’d have covered nearly two-thirds of our most vulnerable segment.

Naturally, we’ll have to deal with a backlog of nearly 300M second doses starting mid-July, but hopefully both vaccine-supply and administrative-capacity will be more plentiful by then. At that point, we’ll need >3M doses/day just for 2nd doses, but that’s around when we expect a step-jump in domestic supply.

Above graph suggests that a delay in administering 2nd doses was inevitable. Purely in terms of managing expectations, it was better to make the delay de jure rather than de facto. With a 12-16 week gap, we’ve given ourselves room to vaccinate twice as many individuals over the next few months.

PS. I’m not aiming for shallow criticism of recent slowdown in vaccinations, frustrating as it is. As always, context matters. Between end-March and early-May, our deaths/day increased 12x and nearly all states locked down. Amidst this vertical spike, it’s unfair to assume that vaccine chain is immune or to expect more from those in the front-line who’re already stretched beyond limit. As an illustration, Bharat Biotech is trying to scale production even as 50 of their employees are down with covid. Debugging how to boost vaccination pace is better done when context is less abnormal (I’ll still be unqualified to do so).

PPS. Extending 2nd dose gap only applies to Covishield, not Covaxin (stays 4 weeks). Since it’s 90:10 between the two, I have ignored this nuance. My numbers could be off by 10% on this account.